Summary of Heinrich Event and modeling of Heinrich Events
Jennifer Hayek
Heinrich events are defined by layers rich in ice rafted debris in the North Atlantic sediment cores due to large amounts of ice having discharged into the ocean during these periods. Specifically foraminifers, minute single celled organisms with calcareous shells are found in the sediment. Also N. pachyderma a species with specific preferences to the type of water it lives in is also correlated with Heinrich events. The six Heinrich events all occurred within the last glacial at time intervals which get progressively closer together towards the present. These events are superimposed on the Dansgaard-Oeschger Events. Dansgaard-Oeschger Eventsoccurmore frequently than Heinrich events causing climate fluctuations which warm the northern hemisphere quickly and than cool it more slowly.
There are several theories on Heinrich Events.
Theory 1:Concerns the internal physics of the ice sheet. The sea surface temperature decreases triggering the amount of N. pachyderma to rise triggering an iceberg discharge.
Theory 2: Salt Oscillator (mechanism in the movie the day after tomorrow) Increased THC induces increased ice sheet growth which creates increased freshwater discharge which decreases THC.
Theory 3:Binge-Purge Mechanism:First, the ice sheet grows by snow accumulation. Then, the sediment below the ice sheet thaws, becomes slippery and a lubricated a pathway in the Hudson straight which icebergs follow into the Labrador Sea. The B-P Mechanism does not explain how the Heinrich events get closer together with time.
Physics Behind Binge-Purge Mechanism:
Fgeo=geothermal forcing
K= thermal conductivity
Ts=temperature at surface
Tb=temperature at bottom of ice (Note this is 0 degrees Celcius for calving and lubrication to occur)
To=temperature above surface
Г= adiabatic lapse rate in air
H=Scale height
γ= lapse rate in ice
accumulation=25cm/year
Fgeo=0
Modeling of Dansgaard Oeschger Oscillation and Heinrich Event (Ganopolski, A, & Rahmstorf S)
The modeling shown was done by taking the continents and ocean volume as large rectangular blocks. The THC as well as fresh water circulation are taken into account.
It is shown that today's climate is in a warm stable mode. During glacial periods the cold phase is the normal phase whereas the warm phase is an anomaly and only marginally stable. The cold phase with a collapsed THC is also a stable mode. A D-O event is just a warm mode superimposed on a cold phased climate. Note that this mode is unstable.
During a H-E fresh water anomaly is very positive, the NADW (North Atlantic Deep Water) is low and so is the temperature. During a D-O event the fresh water anomaly is also positive the NADW is sinking and the temperature is warm but cools afterwards.